A laser robot, particularly a well-known multi-articulated laser robot having freedom of motion about six axes, is provided with a robot wrist, i.e., one of the movable elements of the robot, attached to the extremity thereof. The robot is further provided with an additional-axis mechanism including two drive motors and moves a laser beam projecting unit along a predetermined path, i.e., a feed path, in a biaxial coordinate plane using the additional motion-axis mechanism. Such a laser robot capable of forming a precision small hole in a workpiece by feeding the laser beam projecting unit along a circular feed path having a small diameter has been proposed and put into practical use for laser-beam machining.
A multi-articulated laser robot provided with the above-mentioned additional motion-axis mechanism has a robot unit as shown in FIG. 1, and the operation of the robot unit is controlled by a well-known robot controller for implementing the desired laser-beam machining.
The robot unit 1 has a robot base 2, a robot body 3 set upright on the robot base 2, a turning robot body 4 turnably joined to the upper part of the robot body 3, a robot upper arm 5 pivotally joined for rotating about a horizontal axis to one end of the turning robot body 4, a robot forearm 6 pivotally joined, for rotating about a horizontal axis relative to the robot upper arm 5, to the extremity of the robot upper arm 5, a robot wrist 7 having three degrees of freedom of motion, joined to the extremity of the robot forearm 6 and capable of rotatinging about three axes perpendicular to one another in a three-dimensional space, and an additional motion-axis mechanism 8 attached to the robot wrist 7 and holding a laser-beam machining head 9 including a laser beam projecting device that projects a laser beam for laser-beam machining.
The additional motion-axis mechanism 8 is provided with two built-in drive motors, such as servomotors, not shown, and controls the laser-beam projecting nozzle 9a of the laser-beam machining head 9 for movement, for example, along a desired path in an orthogonal biaxial coordinate plane according to commands provided by the robot controller so as to carry out laser-beam machining of a workpiece by the use of a laser beam for cutting, boring and such.
The additional motion-axis mechanism 8 is mainly used as a mechanism specially for forming small holes with the laser-beam machining head 9. The additional motion-axis mechanism 8 holds the laser beam projecting nozzle 9a at a predetermined position of origin while the movable elements of the six-axis system (the revolving robot body 4, the robot upper arm 5, the robot forearm 6 and the robot wrist 7) of the robot unit 1 are in operation, and the two drive motors of the additional motion-axis mechanism 8 are actuated after the laser beam projecting nozzle 9a of the laser-beam machining head 9 has been positioned by the robot unit 1 at the center of a small hole to be formed so as to move the laser beam projecting nozzle 9a of the laser-beam machining head 9 along a machining locus, such as a circular locus, corresponding to the circumference of the desired small hole to form the small hole by laser-beam machining.
When feeding the laser beam projecting nozzle 9a of the laser-beam machining head 9 to form such a small hole, the additional-axis mechanism 8 positions and stops the laser beam projecting nozzle 9a at a position of origin, moves the laser beam projecting nozzle 9a for a straight approach travel from the origin position to a position corresponding to a point on a desired machining locus, and then feeds the laser beam projecting nozzle 9a along the desired machining locus to complete the operation of laser-beam machining.
Generally, in such a laser-beam machining process, the workpiece is initially pierced therethrough by a laser beam, and then the laser beam projecting nozzle 9a is moved along the machining locus to cut the workpiece by the laser beam. A laser-beam machining method shown in FIG. 6 carries out piercing at the position of origin and another laser-beam machining method shown in FIG. 7 carries out piercing at a predetermined piercing position near a desired machining locus, such as a position where the edge of a through-hole formed by piercing by the laser beam does not cross the machining locus, moves the laser beam for an approach travel toward the machining locus, and then, moves the laser beam along a machining locus for laser-beam machining.
The former laser-beam machining method moves the laser beam projecting nozzle 9a of the laser-beam machining head 9 from the position of origin to a position corresponding to a point on the desired machining locus at a predetermined comparatively low machining speed along a straight path for an approach travel, and then moves the laser beam projecting nozzle 9a along the machining locus at a low machining speed for laser-beam machining. Therefore, this laser-beam machining method takes more machining time and hence the machining efficiency, i.e., machining rate, is rather low.
The latter laser-beam machining method moves the laser beam projecting nozzle 9a at a quick-feed speed from the origin position to the predetermined piercing position near the desired machining locus, carries out piercing at the piercing position, and then carries out laser-beam machining at a machining speed lower than the quick-feed speed. Therefore, this laser-beam machining method is seemingly able to carry out laser-beam machining at an improved machining efficiency. Practically, it is not necessarily true that the latter laser-beam machining method is able to complete a laser-beam machining process in less time than that required by the former laser-beam machining method, because the latter laser-beam machining method needs to position the laser beam projecting nozzle 9a at the predetermined piercing position near the machining locus and needs to execute more positioning operations than the former laser-beam machining method.
Accordingly, the selection of either a laser-beam machining method that starts laser-beam machining from the position of origin at a low machining speed and continues laser-beam machining without increasing the low machining speed or a laser-beam machining method that moves the laser beam projecting nozzle at a quick-feed speed from the position of origin to the predetermined piercing position on the approach path, and then carries out laser-beam machining at a low machining speed has been determined by the operator by a trial-and-error method or by a rule of thumb. The above-mentioned selection of a laser-beam machining method has the inevitable disadvantage that the laser-beam machining cannot be carried out at the highest possible machining efficiency.
The selection of a laser-beam machining method by the operator by a trial-and-error method or by a rule of thumb is an impediment to the promotion of automation of laser-beam machining by means of a laser robot.